1. Field of the Invention
Structures and methods consistent with the present invention relate to a micro-electro-mechanical system (MEMS)-based micro speaker, and more particularly, to a structure of a micro speaker and a fabricating method thereof.
2. Description of the Related Art
Thanks to rapid advancement of terminals for voice and data communications, smaller and diversified terminals have been provided, with the ability to exchange greatly increased amount of data. These terminals are now required to be slimmer, without compromising the existent performance.
In order to meet such customer demands, many have researched acoustic devices using MEMS, for applications in various fields such as otophone, cellular phones, or PDAs. The applications of MEMS and semiconductor technologies to the fields of acoustic devices such as microphones or micro speakers, have achieved product miniaturization, cost reduction, and compatibility to enable integration with the neighboring circuits.
Mainly, the condenser type and piezoelectric type are used to fabricate the MEMS-based microphones and micro speakers. The piezoelectric type is generally applied to the micro speaker, since this enables a simple structure and fabricating process, omits a need for polarization voltage, and provides a wider frequency response range.
A general piezoelectric speaker is constructed in a manner in which a thin membrane is bonded onto a substrate by vapor-deposition for support, the lower electrode, piezoelectric material, and upper electrodes are bonded on one another in turn by vapor-deposition, and then the back surface of the substrate is etched to form a diaphragm structure.
FIG. 1 illustrates a general piezoelectric micro speaker as an example, before packaging, in which a substrate 1 is provided, support layer 2, a lower electrode 3, a piezoelectric material 4, and an upper electrode 5 are bonded thereon in stack structure by vapor-deposition, and the back surface 6 of the substrate 1 is etched to form a diaphragm structure.
Such piezoelectric micro speaker requires a packaging to be mounted to a designated system, to enable wiring of electric input and output, and to protect the system from outside. For example, additional processes and costs are necessary for the packaging, to protect the active surface that radiates sound, or to protect the back surface for vent holes.